Technical Field
Exemplary aspects of the present invention generally relate to a driving force transmission unit to transmit a rotary driving force from a drive source to a target and an image forming apparatus including the driving force transmission unit, and more particularly to an image forming apparatus such as a copier, a facsimile machine, or a printer.
Description of the Related Art
Generally, a driving force transmission unit includes a connecting mechanism that connects a drive shaft on a drive side and a driven shaft on a drive target side such as a roller and a drum. The connecting mechanism is generally provided on a transmission path through which a rotary driving force from a drive source is transmitted to the drive target. Such a known connecting mechanism consists of a pair of couplings (also known as joints) with contact portions at shaft end portions of the drive shaft and the driven shaft facing each other that contact upon transmission of rotary driving force. The contact portions include claws or concave and convex portions that contact one another upon transmission of rotary driving force.
In another known driving force transmission unit, in order to transmit the rotary driving force from the drive shaft to the coupling on the drive side while the axis of the coupling on the drive side is aligned with the drive shaft, the outer circumferential surface of the drive shaft has a rounded rectangular shape in cross-section and the inner circumferential surface of the coupling on the drive side in which the drive shaft is inserted has a rounded rectangle hole in cross-section. The axis of the drive shaft and the axis of the coupling on the drive side are aligned with respect to the shaft portion of the drive shaft having a circular arc shape in cross section and a hole of the coupling on the drive side having a circular arc shape in cross section. The rotary driving force is transmitted from the drive shaft to the coupling on the drive side through the linear-shaped portion of the drive shaft in cross-section and the linear-shaped portion of the hole of the joint on the drive side. As the drive shaft rotates, the rotary driving force is transmitted to the coupling via the linear shaped portions of the drive shaft and the hole of the coupling.